57-year-old Singh was on his way to Singapore for regular health check-up when he fainted at the Dubai airport, an aide at his Delhi residence said.

"His condition is critical but stable," the aide said, adding he has been admitted to Welcare Hospital in Dubai.

Singh, once the public face of Samajwadi Party, was admitted to Singapore's Mount Elizabeth Hospital and Medical Centre for treatment of kidney ailment a couple of years ago. Since then, he has been visiting the facility for regular check up.